ABSTRACT

For the conservation of mangrove forests, management plans should be prepared after evaluating the decreases of mangrove forests explicitly. Although information regarding stand development in mangrove forests is indispensable, there is a lack of it. We reasoned that gathering three-dimensional point cloud data using stabilized cameras and photogrammetry (developed together with unmanned aerial vehicles) could be used to conduct a survey of the sizes and spatial distribution of individual trees in mangrove forests. We surveyed two mangrove forests growing at the mouth of the Okukubi and Ōura rivers on Okinawa Island. The forest floor was photographed using a GoPro Hero 4 attached to a camera stabilizer on about 2- m- long extension pole. The resulting images were processed with a photogrammetry software to create an orthomosaic image. The trunks of trees and seedlings in all plots were visually interpreted. The total number of the seedlings and trees in each plot was counted, and the density in each plot was calculated. The diameter at breast height (DBH) of the trees was calculated from the area of the polygons drawn around the trunks manually. There was a strong correlation between the interpreted and measured DBH. We confirmed the effectiveness of a method that uses stabilized cameras and photogrammetry to survey the size and distribution of individual trees in a mangrove forest. The information obtained by present study is considered to be an essential forest inventory of mangrove forests.

摘要

为了保护红树林，应在明确评估红树林减少后制定管理计划。尽管关于红树林的林分发展的信息是必不可少的，但仍然缺乏。我们认为，使用稳定的相机和摄影测量法（与无人飞行器一起开发）收集三维点云数据可用于对红树林中单个树木的大小和空间分布进行调查。我们调查了冲绳岛奥库比河和Ōura河河口生长的两种红树林。使用安装在约2米长的延长杆上的相机稳定器上的GoPro Hero 4对森林地面进行拍照。所得到的图像用摄影测量软件进行处理以创建正马赛克图像。所有地块的树木和幼苗的树干都通过视觉进行了解释。计算每个样地中的幼苗和树木的总数，并计算每个样地中的密度。通过手动在树干周围绘制多边形的面积来计算树木的胸高（DBH）直径。解释的和测量的DBH之间有很强的相关性。我们证实了使用稳定的相机和摄影测量法测量红树林中单个树木的大小和分布的方法的有效性。通过本研究获得的信息被认为是红树林的重要森林资源。通过手动在树干周围绘制多边形的面积来计算树木的胸高（DBH）直径。解释的和测量的DBH之间有很强的相关性。我们证实了使用稳定的相机和摄影测量法测量红树林中单个树木的大小和分布的方法的有效性。通过本研究获得的信息被认为是红树林的重要森林资源。通过手动在树干周围绘制多边形的面积来计算树木的胸高（DBH）直径。解释的和测量的DBH之间有很强的相关性。我们证实了使用稳定的相机和摄影测量法测量红树林中单个树木的大小和分布的方法的有效性。通过本研究获得的信息被认为是红树林的重要森林资源。